Method, computer program, controller and network node

ABSTRACT

A method of detecting interference caused by inter-modulation in a network node site comprising a set of network nodes for wireless communication capable of communication with a set of stations for wireless communication. The stations are wireless transceiver devices and communication from the network node to any of the stations is considered to be downlink communication and communication from any of the stations is considered to be uplink communication. The method comprises determining a received input signal interference level on at least a part of communication resources for uplink communication, determining a transmitted signal level on at least a part of communication resources for downlink communication, wherein the at least part of communication resources for downlink communication corresponds in time with the at least part of communication for uplink communication, correlating the determined received input signal interference level and the determined transmitted signal level at corresponding time instants to determine a correlation, and determining whether significant interference caused by inter-modulation is present based on the correlation. A computer program, a controller and a network node are also disclosed.

This application is a continuation of U.S. application Ser. No.14/432,054, filed 27 Mar. 2015, which was the National Stage ofInternational Application No. PCT/EP2015/052515, filed 6 Feb. 2015, thedisclosures of all of which are incorporated by reference herein intheir entirety.

TECHNICAL FIELD BACKGROUND

The present invention generally relates to methods for a network node, acontroller, a network node, and a computer program for implementing themethod. In particular, the present invention relates to detectinginterference caused by inter-modulation.

BACKGROUND

In wireless communication systems, interference by radio frequency (RF)transmitters for RF communication systems may become an issue.

The purpose of a transmitter in a digital wireless communication systemis to convert a digital low-frequency baseband signal into an RF signalwhile preserving the modulation, and thereby the baseband information.In a full duplex system, a radio receives and transmits informationsimultaneously, which may be performed according to frequency duplexdivision (FDD), i.e. the radio transmits on one frequency and receiveson another frequency. This means that, despite the fact that receive(RX) and transmit (TX) signals are spaced in frequency by a duplexdistance, distortion products caused by nonlinearities in thetransmitter may fall into the receive band and raise the over-allreceiver noise figure, as well as discomply with a transmit spectrummask. In order to reduce this effect, external cavity filters may beused in radio base stations (RBS) to filter out unwanted componentsoutside wanted transmission band. However, intermodulation productscaused by multiple transmitted signals, e.g. own TX signal incombination with an interferer signal, may also position unwanted tonesin the receive band and thus degrade the receiver signal-to-noise-ratio(SNR). These unwanted tones are not possible to filter out by frequencyfiltering and they are thus to be handled by the receiver.

In a multi operator FDD RBS site solution, each operator uses a uniquepaired spectrum and the spectrum parts thus become separated infrequency not to interfere with each other's operations. There is nojoint scheduling required among the operators, resulting in thatsimultaneous transmissions may occur. However, due to non-linear effectscaused by for instance excitation of ferromagnetic materials or otherphysical properties, e.g. metal oxidation, mechanical disruptions, etc.,passive intermodulation (PIM) products may be reflected back to orwithin the RBS site and fall into one of the operator's receive band andcause desensitization. As a result, the created PIM products caused bythe multi operator transmissions may result in lowered received uplinkSNR for some scenarios. The problem may also arise in the case when thesame operator uses two different carrier frequencies, e.g. operating incarrier aggregation setup, in any direction. The problem may also affector be affected by frequencies used for time division duplex (TDD) uponsuch relations between frequencies.

A normal operation to handle such problems would be to send a servicetechnician to the RBS site to try to find the cause and replace or mendthe causing element. However, such an operation may take a while, andthere may be a not fully functioning RBS for a longer or shorter time.

In the case when two FDD downlink bands are separated by the samefrequency distance as the duplex distance for one of the FDD receiverfrequencies, third order PIM products may become collocated within areceive band without the possibility to be suppressed by filtering asdiscussed above. As a result, the noise level of the affected receiverwill increase and lower received SNR in the uplink.

An example is illustrated in FIG. 1 where two transmitted signals 100,102, for example 3GPP frequency band 29 and band 17, from the same RBSgive rise to a PIM product 104, in this case due third orderintermodulation, i.e. at 2·f1−f2, where f1 is the frequency oftransmission in B17 and f2 is the transmission frequency in band 29,falling into the receive band 106 of band 17. As a result, in the band17 the receiver will lower its sensitivity and face reduced coverage.Continuing this example with reference to FIG. 2, a base station 200 isoperating a cell 202. The lowered sensitivity will decrease the possiblecoverage of the cell to a limited coverage 204. This could potentiallylead to dropped connections or limited application coverage asillustrated by UE A 206 in FIG. 2, while for UEs closer to the networknode 200, e.g. UE B 208, the communication may still work. This may leadto the operator missing traffic (to be billed) and/or less satisfactionby subscribers.

This may become more and more of a problem the more bands that areavailable, since with the more bands there will be larger risks forco-sited RBSs for different operators, which may create PIM affectingany of the operators' receive bands. For the sake of brevity and easierunderstanding, the issue has been demonstrated above whereinter-modulation is caused by two frequencies, but the similar effectsmay arise from further used frequencies, and used frequenciesinter-modulating with inter-modulation products, and so on. That is, themore frequencies used at a network node site, the more likely is it thatan inter-modulation product affects a receive band.

It is therefore a desire to detect such situations to be able to handlethem.

SUMMARY

The invention is based on the understanding that the above situation mayor may not occur depending on situations that are hard to predict, e.g.the case of intermodulation caused by occurred metal oxidation. Toestimate whether the situation has occurred, the inventors suggest anapproach including correlating collected statistics.

According to a first aspect, there is provided a method of detectinginterference caused by inter-modulation in a network node sitecomprising a set of network nodes for wireless communication capable ofcommunication with a set of stations for wireless communication. Thestations are wireless transceiver devices and communication from thenetwork node to any of the stations is considered to be downlinkcommunication and communication from any of the stations is consideredto be uplink communication. The method comprises determining a receivedinput signal interference level on at least a part of communicationresources for uplink communication, determining a transmitted signallevel on at least a part of communication resources for downlinkcommunication, wherein the at least part of communication resources fordownlink communication corresponds in time with the at least part ofcommunication for uplink communication, correlating the determinedreceived input signal interference level and the determined transmittedsignal level at corresponding time instants to determine a correlation,and determining whether significant interference caused byinter-modulation is present based on the correlation.

The method may further comprise selecting the at least a part ofcommunication resources for uplink communication.

The at least a part of communication resources for uplink communicationmay exclude any data transmission.

The at least a part of communication resources for uplink communicationmay exclude any data transmission by not scheduling any of the set ofstations to transmit any uplink communication to any of the networknodes during the at least a part of communication resources.

The at least a part of communication resources for uplink communicationmay exclude any data transmission by selecting the at least a part ofcommunication resources to be at times when the set of stations onlytransmits reference signals.

The transmitted signal may be provided at a selected level for eachinstant. The selected level may be at substantially full transmit powerlevel for the network node transmitting the signal for at least someinstant. The selected level may be at substantially minimum transmitpower level for the network node transmitting the signal for at leastsome instant. Significant interference caused by inter-modulation may beconsidered present based on the correlation when correlation betweensubstantially full transmit power level for the network node and ahigher received input signal interference level and correlation betweensubstantially minimum transmit power level for the network node areabove a threshold.

The method may comprise providing the determined received input signalinterference level and transmitted signal level to a statisticsmechanism, and receiving the statistics to be correlated from thestatistics mechanism.

The method may comprise taking a predetermined action when significantinterference caused by inter-modulation is determined to be present.

According to a second aspect, there is provided a computer programcomprising instructions which, when executed on a processor of acommunication apparatus, causes the communication apparatus to performthe method according to the first aspect.

According to a third aspect, there is provided a controller arranged tooperate with a network node site comprising a set of network nodes forwireless communication capable of communication with a set of stationsfor wireless communication. The stations are wireless transceiverdevices and communication from the network node to any of the stationsis considered to be downlink communication and communication from any ofthe stations is considered to be uplink communication. The controllercomprises an interference level detector arranged to determine areceived input signal interference level on at least a part ofcommunication resources for uplink communication, a transmit signallevel monitor arranged to determine a transmit signal level on at leasta part of communication resources for downlink communication, whereinthe at least part of communication resources for downlink communicationcorresponds in time with the at least part of communication for uplinkcommunication, a correlator arranged to correlate the determinedreceived input signal interference level and the determined transmittedsignal level at corresponding time instants to determine a correlation,and an analyser arranged to determine whether significant interferencecaused by inter-modulation is present based on the correlation.

The controller may further comprise a scheduler arranged to select theat least a part of communication resources for uplink communication.

The at least a part of communication resources for uplink communicationmay exclude any data transmission.

The at least a part of communication resources for uplink communicationmay exclude any data transmission by disabling scheduling of any of theset of stations to transmit any uplink communication to any of thenetwork nodes during the at least a part of communication resources.

The at least a part of communication resources for uplink communicationmay exclude any data transmission by selecting the at least a part ofcommunication resources to be at times when the set of stations onlytransmits reference signals.

The controller may be arranged to provide control such that thetransmitted signal is provided at a selected level for each instant. Theselected level may be at substantially full transmit power level for thenetwork node transmitting the signal for at least some instant. Theselected level may be at substantially minimum transmit power level forthe network node transmitting the signal for at least some instant. Theanalyser may be arranged to consider significant interference caused byinter-modulation to be present based on the correlation when correlationbetween substantially full transmit power level for the network node anda higher received input signal interference level and correlationbetween substantially minimum transmit power level for the network nodeare above a threshold.

The controller may comprise an interface arranged to provide thedetermined received input signal interference level and transmittedsignal level to a statistics mechanism, and receive the statistics to becorrelated from the statistics mechanism.

The controller may be arranged to enable a predetermined action whensignificant interference caused by inter-modulation is determined to bepresent.

According to a fourth aspect, there is provided a network node forwireless communication capable of communication with a set of stationsfor wireless communication comprising a controller according to thethird aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 schematically illustrates how inter-modulation issues may degradea signal.

FIG. 2 schematically illustrates a base station operating a cell and howinter-modulation degradation may limit the range of the base station.

FIG. 3 is a flow chart illustrating a method of detecting interferencecaused by inter-modulation in a network node for wireless communicationaccording to an embodiment.

FIG. 4 is a block diagram schematically illustrating a network nodeaccording to an embodiment.

FIG. 5 is a block diagram schematically illustrating a network node siteaccording to an embodiment.

FIG. 6 schematically illustrates a computer-readable medium and aprocessing device.

FIG. 7 schematically illustrates functional elements for handlinginterference caused by inter-modulation in a network node for wirelesscommunication according to an embodiment.

DETAILED DESCRIPTION

Methods of detecting interference, a network, NW, node and computerprograms for the same are disclosed below. The interference on topic iscaused by inter-modulation in a NW node, or NW node site comprising aplurality of co-located NW nodes, for wireless communication with a setof stations for wireless communication. The term “co-located” should inthis context include that the network nodes are located in the same spotor housing, as well at being in close neighbourhood such that signalsfrom the network nodes may cause intermodulation products as discussedabove. A station in this context may for example be a user equipment,UE, a modem, a cellphone, a computer or, any electric or electronicdevice capable of wireless communication with a NW node. More and moreitems we previously knew as rather simple objects are now capable ofthis, which has, and will, provide for some of the great improvements inmany fields, even outside the conventional telecommunication industry.Examples are sensors, machines, medical equipment, monitoring devices,etc. that has been enhanced by being able to wirelessly communicate withwireless nodes of different wireless communication systems.

In this disclosure below, embodiments are exemplified within an 3GPP LTEcontext for the sake of easier understanding, but the invention is notlimited to that Radio Access Technology (RAT). Other RATs, such as anyof the commonly used technologies for public land mobile networks, maybenefit from the invention in a similar way.

FIG. 3 is a flow chart illustrating methods of embodiments. The methodincludes determining 300 received input signal interference level onuplink, UL, communication resources. The UL communication resources maycorrespond to an entire transmission time interval or selected partsthereof. The selected parts thereof may be selected such that thoseparts do not include any data transmission which facilitates thedetermination of the interference level since the nominal signal levelof the received signal then is reasonably known. If determination is tobe made on signals including data transmissions, the determination mayrely on statistics or other information to estimate the interferencelevel. The determination 302 of interference level may also include“active” silence, i.e. the method may arrange that no schedule for anuplink transmission grant for the stations is made during a particulartransmission time interval, wherein all of the received signal is somekind of interference.

The method also includes determining 302 a transmitted signal level onat least a part of communication resources for downlink communication.The at least part of communication resources for downlink communicationshould correspond in time with the at least part of communication foruplink communication to be able to determine if the transmitted signalaffects the interference level of the received signal. The correspondingtime may for example be defined by corresponding subframes ortransmission time intervals.

Both the received signal and the transmitted signal should be knownand/or under control of the entity performing the method. This may bethe case when the entity is one network node. This may also be the casewhen more than one network node, where one does the receiving andanother does the transmitting referred to above, are involved but areunder control by e.g. a common controller. A network node in thiscontext may operate on one or more frequency bands, e.g. one frequencyband for both receiving and transmitting, one frequency band fortransmitting and receiving and another frequency band for transmittingor receiving, or one or more frequency bands for respective transmittingand receiving. Thus, the network node(s) may operate in time divisionduplex, TDD, frequency division duplex, FDD, and/or with carrieraggregation, wherein different relations may occur when a receivedchannel may be interfered by inter-modulation from a transmitted channelin a network node site comprising a set of network nodes, i.e. one ormore, capable of wireless communication with a set of stations forwireless communication.

For determining such relations where the received signal is interferedby inter-modulation introduced by a transmitted signal which is undercontrol by the entity performing the method, the method correlates 304statistics from the determined received input signal interference leveland the determined transmitted signal level. This may be performed forany relations between received signals and transmitted signals which areunder control by the entity performing the method.

Based on the correlations, it is determined 306 whether significantinterference is caused by inter-modulation introduced by the transmittedsignal which is under control by the entity performing the method. Ifsuch significant interference is determined present, a predeterminedaction may be taken 307. The predetermined action may for exampleinclude assigning communication resources such that communication isless affected by the interference.

The determination whether significant interference is caused, as statedabove, may include comparing 305 a correlation metric value provided bythe correlation 304 with a threshold, wherein a correlation metric valueexceeding the threshold indicates that the significant interference ispresent while if the correlation metric value is below the threshold,the method continues to monitor 300, 302 received input signalinterference levels and transmit signal levels.

Statistics based on the received input signal interference levels andtransmitted signal levels may be collected 303 over time, as indicatedby the arrow returning to the determination step 300, to providesufficient statistics to correlate 304. The statistics may be collected303 locally or may be collected 303 by aid of remote elements comprisingdatabase and processing means. For example, the element performing themethod may comprise an interface arranged to provide the determinedreceived input signal interference level and transmitted signal level toa statistics mechanism of the remote element, or a statistics mechanismof the element performing the method. For making the correlation thecorrelation 304, the statistics to be correlated are received from thestatistics mechanism and the correlations are done 304 thereon.

The monitoring and building of statistics may for example be an ongoingprocess as transmissions and receptions are performed in the networknode site while the correlating and determining may be performedperiodically. However, the monitoring and building of statistics mayalso be made periodically, wherein the period for monitoring may beequal or shorter than the period for the correlating and determiningwhether significant interference is present.

To enhance the statistics, it may be desired to provide a variety oftransmit signal levels to the monitored set. Therefore, transmission onthe DL communication resources may be assigned 301 such that thisvariation is achieved. This may comprise selecting the transmit level toe.g. substantially full transmit power level for the network nodetransmitting the signal for at least some of the time instants, andsubstantially minimum transmit power level for the network nodetransmitting the signal for at least some of the time instants. Fulltransmit power level may for example be provided by ensuring that thecommunication resources, which may be defined by time, frequency and/orcode, are completely filled, which may require filling with dummyinformation. Minimum transmit power level may for example be provided byonly transmitting mandatory reference signals etc. and possibly withreduced power level, i.e. not scheduling any traffic on thecommunication resources in question. The variation may also be achievedby normal variation in transmissions. The determination 302 oftransmitted signal level may for example be provided from information onutilization of the communication resources.

FIG. 4 is a block diagram schematically illustrating a NW node 400according to an embodiment. The NW node 400 comprises an antennaarrangement 402, a receiver 404 connected to the antenna arrangement402, a transmitter 406 connected to the antenna arrangement 402, aprocessing element 408 which may comprise one or more circuits, one ormore input interfaces 410 and one or more output interfaces 412. Theinterfaces 410, 412 can be user interfaces and/or signal interfaces,e.g. electrical or optical. The NW node 400 is arranged to operate in acellular communication network, e.g. as a base station operating a cell.In particular, by the processing element 408 being arranged to performthe embodiments demonstrated with reference to FIGS. 2 and 3, the NWnode 400 is capable of detecting inter-modulation interference issues.The processing element 408 can also fulfill a multitude of tasks,ranging from signal processing to enable reception and transmissionsince it is connected to the receiver 404 and transmitter 406, executingapplications, controlling the interfaces 410, 412, etc.

The NW node 400 comprises controller 414 arranged to handle somespecific functions related to the method demonstrated above. Thecontroller may be a separate element or be integrated in the processor408. The controller 414 comprises an interference level detectorarranged to detect a received input signal interference level on atleast a part of communication resources for uplink communication in auplink carrier frequency band. The interference level detector is thusconnected to the receiver 404 to be able to gain levels and informationfor performing its task. The controller 414 further comprises a transmitsignal level monitor arranged to determine a transmit signal level on atleast a part of communication resources for downlink communication. Thetransmit signal level may be determined from output of the transmitter406, or be determined based on inputs and settings provided to or withinthe transmitter 406. At least part of communication resources fordownlink communication corresponds in time with the at least part ofcommunication for uplink communication such that they may be analysed,as demonstrated above and also shown below. The controller 414 furtherincludes a correlator arranged to correlate statistics from thedetermined received input signal interference level and the determinedtransmitted signal level, and an analyser arranged to determine whethersignificant interference caused by inter-modulation is present based onthe correlation.

By these elements it is possible to determine whether the interferencelevel indicates significant inter-modulation interference caused bytransmissions made by the transmitter 406, i.e. by collecting statisticsand performing correlation and evaluating them. The controller 414 maythus be considered to perform the steps 300 and 302 of FIG. 3 to enablecollection of interference and signal levels for the statistics asdemonstrated above, wherein the controller 414 is able to determine, byperforming the correlations from the collected statistics, ifsignificant inter-modulation issues caused by signals transmitted by thetransmitter 406 exist. The controller 414 may further be arranged to, if“active” silence is required on the uplink for the measurements, arrangethat no schedule for an uplink transmission grant for the stations ismade. The uplink transmission grant is valid for a future TTI. Thecontroller 414, which is connected to the transmitter 406, may furtherbe arranged to avoid the uplink transmission grant to the stations, andto allocate a transmit level on the downlink carrier frequency band atthe future TTI such that measurements to collect desired statistics oninter-modulation interference is enabled on the uplink carrier frequencyband. The controller 414 is illustrated as a separate functionalelement, but may be implemented within the processing element 408 insome embodiments. This will be further demonstrated with reference toFIG. 7.

FIG. 5 is a block diagram schematically illustrating a NW node site 500according to an embodiment. The NW node site 500 comprises two or moreco-located NW nodes 501 a, 501 b and a NW node site controller 520. TheNW nodes 501 a, 501 b resembles the NW node 400 demonstrated withreference to FIG. 4. That is, the NW nodes 501 a, 501 b each comprisesan antenna arrangement 502 a, 502 b, a receiver 504 a, 504 b connectedto the antenna arrangement 502 a, 502 b, a transmitter 506 a, 506 bconnected to the antenna arrangement 502 a, 502 b, a processing element508 a, 508 b which may comprise one or more circuits, one or more inputinterfaces 510 a, 510 b and one or more output interfaces 512 a, 512 b.The antenna arrangements 502 a, 502 b may be a common antennaarrangement for the network nodes 501 a, 501 b. The interfaces 510 a,510 b, 512 a, 512 b can be user interfaces and/or signal interfaces,e.g. electrical or optical. The NW nodes 501 a, 501 b may be arranged tooperate in a cellular communication network, e.g. as a base stationoperating a cell. The processing element 508 a, 508 b can also fulfill amultitude of tasks, ranging from signal processing to enable receptionand transmission since it is connected to the receiver 504 a, 504 b andtransmitter 506 a, 506 b, executing applications, controlling theinterfaces 510 a, 510 b, 512 a, 512 b, etc. The NW nodes 501 a, 501 beach may comprise a controller 514 a, 514 b arranged to detect aninterference level on the uplink carrier frequency band for a subset ofstations of the set of stations. The controllers 514 a, 514 b are thusconnected to the receivers 504 a, 504 b, respectively, to be able togain levels and information for performing its task. The controllers 514a, 514 b are illustrated as separate functional elements, but may beimplemented within the processing elements 508 a, 508 b or in the commonNW node site controller 520 in some embodiments. The controllers 514 a,514 b may alternatively be considered to be more or less only interfacestowards the NW node site controller 520 which may perform theactivities. Alternatively, the NW node site controller 520 may beconsidered to be more or less only an interface between the controllers514 a, 514 b, which may perform the activities and exchange necessaryinformation via the NW node site controller 520, i.e. the functions ofthe NW node site controller 520 is distributed wherein the NW node sitecontroller 520 per se, at least partially, may be regarded asdistributed, e.g. between controllers 514 a, 514 b, or processingelements 508 a, 508 b.

In the following, the functions related to inter-modulation interferencedetection will be described from the point of view that a first NW node501 a transmits a DL signal which may interfere with an UL signal to asecond NW node 501 b. This applies of course the other way too, but forthe sake of brevity, the explanation is made from the above referencedpoint of view wherein the skilled reader readily understands how it willwork both ways.

The second NW node 501 b is arranged to detect an interference level ona transmission received on an associated uplink carrier frequency bandfor a subset of stations or UEs of a set of stations or UEs associatedwith the second NW node 501 b. By these elements it is possible todetermine whether the interference level indicates significantinter-modulation interference caused by transmissions made by thetransmitter 506 a, i.e. by collecting statistics and performingcorrelation and evaluating them. The controller(s), according to any ofthe task distributions demonstrated above, may thus be considered toperform the method according to any of the embodiments demonstrated withreference to FIG. 3 to enable collection of interference and signallevels for the statistics as demonstrated above, wherein thecontroller(s) is/are able to determine, by performing the correlationsfrom the collected statistics, if significant inter-modulation issuescaused by signals transmitted by the transmitter 506 a exist. Thecontroller(s) may further be arranged to, if “active” silence isrequired on the uplink for the measurements, arrange than no schedulefor an uplink transmission grant for the stations is made. The uplinktransmission grant is valid for a future TTI. The controller 514 b,which is connected to the transmitter 506 b, may further be arranged toavoid the uplink transmission grant to the stations, and to allocate atransmit level on the downlink carrier frequency band at the future TTIsuch that measurements to collect desired statistics on inter-modulationinterference is enabled on the uplink carrier frequency band.

The methods according to the present invention is suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for the case where any of the processing elements408, 414, 508 a, 508 b, 514 a, 514 b, 520 demonstrated above comprises aprocessor handling determination of inter-modulation interference.Therefore, there is provided computer programs, comprising instructionsarranged to cause the processing means, processor, or computer toperform the steps of any of the methods according to any of theembodiments described with reference to FIG. 3. The computer programspreferably comprises program code which is stored on a computer readablemedium 600, as illustrated in FIG. 6, which can be loaded and executedby a processing means, processor, or computer 602 to cause it to performthe methods, respectively, according to embodiments of the presentinvention, preferably as any of the embodiments described with referenceto FIG. 3. The computer 602 and computer program product 600 can bearranged to execute the program code sequentially where actions of theany of the methods are performed stepwise. The processing means,processor, or computer 602 is preferably what normally is referred to asan embedded system. Thus, the depicted computer readable medium 600 andcomputer 602 in FIG. 6 should be construed to be for illustrativepurposes only to provide understanding of the principle, and not to beconstrued as any direct illustration of the elements.

FIG. 7 schematically illustrates functional elements for detectinginterference caused by inter-modulation in a NW node or NW node site forwireless communication according to an embodiment. The technologydemonstrated above is suitably implemented as a combination of softwareand hardware, where the software parts may be performed at one dedicatedprocessor or distributed between two or more processors, which sometimesmay belong to different entities, e.g. between NW nodes of a NW nodesite. FIG. 7 therefore describes an apparatus 700 from a functionalpoint of view where the distribution between processors is arbitrary.The apparatus 700, which may be a NW node or a NW node site asdemonstrated with reference to FIGS. 4 and 5, comprises an UL carrierfrequency band interference level determiner 702, which based on inputfrom one transceiver 710 determines an interference level for an ULcarrier frequency band. The determined interference level is provided tostatistics engine 704 Further, transmit levels are sent from thetransceiver 710 or another transceiver in possession of the operator tothe statistics engine 704. The statistics engine 704 collects statisticson interference levels and transmit levels, as demonstrated above. Thestatistics engine 704 may be internal or external to the network node.The statistics engine 704 provides statistics to a correlator 706 whichcorrelates transmit levels to interference levels at corresponding timeinstants. Correlation metric values are provided to a determinator 708,which from the correlation metric values determines whether atransmitter in possession of the operator causes significantinter-modulation interference reaching the receiver. If such significantinter-modulation interference is determined to be present, an actionhandler 712 may be involved to apply some action for reducing impact ofthe interference. The action handler 712 may affect operation of thetransceiver(s).

What is claimed is:
 1. A method of detecting interference caused byinter-modulation in a network node site comprising a set of networknodes for wireless communication capable of communication with a set ofstations for wireless communication, wherein the stations comprisewireless transceiver devices, wherein communication from the networknode to any of the stations comprises downlink communication, andwherein communication from any of the stations comprises uplinkcommunication, the method comprising: determining a received inputsignal interference level on at least a part of communication resourcesfor uplink communication; determining a transmitted signal level on atleast a part of the communication resources for downlink communication,wherein the at least a part of the communication resources for thedownlink communication corresponds in time with the at least a part ofthe communication resources for the uplink communication; correlatingthe determined received input signal interference level and thedetermined transmitted signal level at corresponding time instants todetermine a correlation; and determining whether significantinterference caused by inter-modulation is present based on a comparisonof a correlation metric value of the correlation with a threshold. 2.The method of claim 1, further comprising selecting the at least a partof the communication resources for the uplink communication.
 3. Themethod of claim 1, wherein the at least a part of the communicationresources for the uplink communication does not include any user data.4. The method of claim 3, wherein the at least a part of thecommunication resources for the uplink communication does not includeany user data by not scheduling any of the set of stations to transmitany uplink communication to any of the network nodes during the at leasta part of the communication resources for the uplink communication. 5.The method of claim 3, wherein the at least a part of the communicationresources for the uplink communication does not include any user data byselecting the at least a part of the communication resources for theuplink communication to be at times when the set of stations onlytransmits reference signals.
 6. The method of claim 1, wherein thetransmitted signal is provided at a selected level for each instant. 7.The method of claim 6, wherein the selected level is at substantiallyfull transmit power level for the network node transmitting the signalfor at least some instant.
 8. The method of claim 6, wherein theselected level is at substantially minimum transmit power level for thenetwork node transmitting the signal for at least some instant.
 9. Themethod of claim 1, wherein significant interference caused byinter-modulation is considered present based on the correlation when thecorrelation exceeds a threshold.
 10. The method of claim 1, furthercomprising taking a predetermined action when significant interferencecaused by inter-modulation is determined to be present.
 11. A computerprogram product stored in a non-transitory computer readable medium forcontrolling a processor circuit of a communication apparatus, thecomputer program product comprising software instructions which, whenrun on the processor circuit of the communication apparatus, causes thecommunication apparatus to: determine a received input signalinterference level on at least a part of communication resources foruplink communication; determine a transmitted signal level on at least apart of the communication resources for downlink communication, whereinthe at least a part of the communication resources for the downlinkcommunication corresponds in time with the at least a part of thecommunication resources for the uplink communication; correlate thedetermined received input signal interference level and the determinedtransmitted signal level at corresponding time instants to determine acorrelation; and determine whether significant interference caused byinter-modulation is present based on a comparison of a correlationmetric value of the correlation with a threshold.
 12. A controllercircuit configured to operate with a network node site comprising a setof network nodes for wireless communication capable of communicationwith a set of stations for wireless communication, wherein the stationscomprise wireless transceiver devices, wherein communication from thenetwork node to any of the stations comprises downlink communication,and wherein communication from any of the stations comprises uplinkcommunication, the controller circuit comprising: an interference leveldetector circuit configured to determine a received input signalinterference level on at least a part of communication resources foruplink communication; a transmit signal level monitor circuit configuredto determine a transmit signal level on at least a part of communicationresources for downlink communication, wherein the at least a part of thecommunication resources for the downlink communication corresponds intime with the at least a part of the communication resources for theuplink communication; a correlators circuit configured to correlate thedetermined received input signal interference level and the determinedtransmitted signal level at corresponding time instants to determine acorrelation; and an analyser circuit configured to determine whethersignificant interference caused by inter-modulation is present based ona comparison of a correlation metric value of the correlation with athreshold.
 13. The controller of claim 12, further comprising ascheduler circuit configured to select the at least a part of thecommunication resources for the uplink communication.
 14. The controllerof claim 12, wherein the at least a part of the communication resourcesfor the uplink communication does not include any user data.
 15. Thecontroller of claim 14, wherein the at least a part of the communicationresources for the uplink communication does not include any user data bydisabling scheduling of any of the set of stations to transmit anyuplink communication to any of the network nodes during the at least apart of the communication resources for the uplink communication. 16.The controller of claim 14, wherein the at least a part of thecommunication resources for the uplink communication does not includeany user data by selecting the at least a part of the communicationresources for the uplink communication to be at times when the set ofstations only transmits reference signals.
 17. The controller of claim12, further configured to provide control such that the transmittedsignal is provided at a selected level for each instant.
 18. Thecontroller of claim 17, wherein the selected level is at substantiallyfull transmit power level for the network node transmitting the signalfor at least some instant.
 19. The controller of claim 17, wherein theselected level is at substantially minimum transmit power level for thenetwork node transmitting the signal for at least some instant.
 20. Thecontroller of claim 12, wherein the analyser circuit is configured toconsider significant interference caused by inter-modulation to bepresent based on the correlation when correlation exceeds a threshold.21. The controller of claim 12, further configured to enable apredetermined action when significant interference caused byinter-modulation is determined to be present.
 22. A network node forwireless communication capable of communication with a set of stationsfor wireless communication, wherein the stations comprise wirelesstransceiver devices, wherein communication from the network node to anyof the stations comprises downlink communication, and whereincommunication from any of the stations comprises uplink communication,wherein the network node comprises a controller circuit comprising: aninterference level detector circuit configured to determine a receivedinput signal interference level on at least a part of communicationresources for uplink communication; a transmit signal level monitorcircuit configured to determine a transmit signal level on at least apart of communication resources for downlink communication, wherein theat least a part of the communication resources for the downlinkcommunication corresponds in time with the at least a part of thecommunication resources for the uplink communication; a correlatorscircuit configured to correlate the determined received input signalinterference level and the determined transmitted signal level atcorresponding time instants to determine a correlation; and an analysercircuit configured to determine whether significant interference causedby inter-modulation is present based on a comparison of a correlationmetric value of the correlation with a threshold.